The recent advancement of radio communication technology has led to implementation of a radio communication system between a mobile communication terminal (Mobile Node), which is capable of establishing connection to multiple radio communication networks employing different radio communication methods, or a mobile router and a mobile communication terminal (Mobile Network Node), which is connected to the mobile router and is joining a mobile network.
Such radio communication system includes: an MIH user (Media Independent Handover User, mobility manager) configured to administrate mobility between multiple radio communication networks; and multiple link controllers each configured to establish a radio link with any one of the radio communication networks.
Proposal has been made to include an MIH function (Media Independent Handover Function, handover controller) between an MIH user and multiple link controllers in such radio communication system capable of establishing connection to multiple radio communication networks, the MIH function being configured to control handover between the radio communication networks, i.e., inter-system handover (non-patent document 1, for example).
In addition, the inventor of the present application has already proposed the following method. In the method, when an MIH function is provided between an MIH user and a link controller, the MIH user notifies the MIH function of a service quality request value, which is a request value of service quality (QoS) in the MIH user (including an upper entity such as a communication application, where a protocol stack of layer 3 or above is also included and an example is a handover manager for handling TCP, UDP, policy or the like), and then the MIH function sets a communication quality threshold of a radio link, in the link controller, the communication quality threshold being associated with the service quality request value notified from the MIH user.
By using such method, when being notified that the communication quality of the radio link has reached the communication quality threshold, by the link controller, the MIH function notifies the MIH user that the communication quality has reached the service quality request value corresponding to the communication quality threshold. Accordingly, the MIH user can quickly decide to change the service quality request value or to perform handover.